It is noted some types of breakdowns on an aircraft, such as undesired movements of control surfaces, incorrect lateral centering, undesired extension of thrust reversers or outside conditions such that a frost accretion difference between right wing and left wing can generate a lateral dissymmetry of the aircraft. Bilateral dissymmetry, it is meant that the default of symmetry between right side and left side of the aircraft, with respect to the median vertical plan of said aircraft.
Such a lateral dissymmetry results in the following effects on the behaviour of an aircraft, in particular a cargo aircraft:                it generates a roll movement which is generally compensated for by control surfaces of the roll axis (ailerons and spoilers); and        it generates a yaw movement which is generally compensated for by control surfaces of the yaw axis (the rudder unit).        
The direction and magnitude of such movements depend on the side of dissymmetry and the type of breakdowns or the outside environmental conditions at the origin of such dissymmetry.
Such dissymmetry is generally compensated for, during a flight, either automatically by an auto-flight device of the aircraft, or manually by a pilot using means for controlling the control surfaces. These actions aim at ensuring some stability to the aircraft and some comfort for passengers. The response of the aircraft to a dissymmetry therefore results in control surface deflections. These control surface deflections generate an additional drag which is proportional to the nature and the level of the dissymmetry to be corrected and which leads to an increase of fuel consumption.
This phenomenon, when maintained for a significant time, leads to a fuel overconsumption and then reduces, in particular, the security margins in term of accessible distance for the aircraft.
Solutions are currently known for treating particular breakdowns generating a lateral dissymmetry, for example engine breakdowns. However, these usual solutions are only adapted to these particular breakdowns for which they were designed.
In addition, they can generate new negative effects required to be overcome. As an illustration, a breakdown of one or more engines located on a same side of an aircraft generates, firstly, a high yaw moment. The latter is mainly compensated for by deflecting the rudder. Yet, such deflection induces, in turn, a roll moment which adds to the effect of the breakdown.
Besides, from document WO-2007/019135, an automated system is known, which detects and records factors influencing the fuel consumption of an aircraft. This system provides detecting and recording configuration factors (such as the engine(s) effectively used on the airplane, the weight, the weight distribution, the engine pressure and the rotation speeds of the engine), environmental factors (such as wind speed and direction, temperature, altitude and air pressure), and flight path factors (such as the effectively travel route, travel distance, and take-off/landing conditions for airports). Functions of this system are the following:                using the obtained data for standardizing the fuel efficiency of each aircraft and engine;        using the standardizing data for an aircraft and engine fleet of an airline, in order to find the optimum aircraft/engine combinations for the routes traveled by the airline; and        sending, from the aircraft, the data collected during a flight or a notification message to a computer system of the airline, in order to download the collected data from the aircraft upon the following landing.        